This invention relates generally to headed fasteners such as screws, bolts and the like, and more particularly, to screws with multi-point wrenching heads having locking capabilities, and locks therefor.
Cap head screws having multi-point wrenching heads may be advantageously used in standard counterbored holes in lieu of sockethead cap screws in that they provide for tighter and faster wrenching. In addition, such fasteners with multi-point wrenching heads are lighter in weight, have less flange width, and are less costly for a given torque requirement. The improved wrenching results because of the external and increased peripheral wrench-engaging surface on the head of the screw which provides for better leverage. More particularly, plural wrenching surfaces are advantageously angled substantially radially and disposed radially outwardly to a greater extent than the wrenching surfaces of socket-head cap screws thereby improving the wrenching angle and leverage which increases substantially the amount of torque that can be applied before the screw head deforms as compared to comparatively sized socket-head cap screws. Accordingly, ultimate product cost, weight and size can be reduced by employing multi-point wrenching screws over socket-head cap screws.
These same advantages will result, although to a lesser degree, by using such fasteners with multi-point wrenching heads in applications other than counterbores. However, in some applications, such as turbines, compressors, engines and the like where the component parts of the assemblies are subject to vibration and shock, it may be necessary to provide a lock for the screws to prevent loosening thereof. Until now no way has been found effectively to lock multi-point wrenching screws in such applications, whereby the less desirable square or hex-head fasteners had to be employed because of their ability to be locked against loosening due to vibrations and like by using such locking devices as locking strips having locking tabs that can be bent against one of the flat driving surfaces of the fastener head to prevent undesired turning of the fastener.